How to choose correct type of lighting

Lighting Basics

Plants eat sunlight, converting the solar energy to chemical throught the process of photosynthesis. And plants, just like us, are what they eat. The spectrum type, length, and intensity all play key roles in vegetative cultivation and overall plant health.

Intensity

Plants will grow tall, elongated stems without enough light because the plant is stretching to find additional energy rather than producing leaves to harness it. For indoor plants, this isn't an option. However, you simply can't drop a 1000 watt lamp over your plants and call it a day, a careful balance must be struck between the amount of light produced and the amount of waste heat generated—too much heat will shrivel plants like Shrinky-Dinks, especially sprouts and young seedlings. For those, Fluorescent bulbs are the superior choice. They produce very little head and therefore can be set very close to the tops of the plants, providing lots of light while keeping the plants from getting leggy or scorching.

Duration

Despite what many amateur closet gardeners will tell you, no plant requires 24-hour sunlight. In fact, all sun and no shade makes Plant a dull boy. Plants perform a fair amount of their vegetative growth during the dark hours changes in the duration of a day affect flowering and fruit production.

Spectrum

Per Wikipedia, "The color temperature of a light source is the temperature of an ideal black-body radiator that radiates light of comparable hue to that of the light source." Colors above 5000K are known as cool colors (blue) and closely resemble natural sunlight. Colors below 3,000K are known an warm colors (red). The spectrum of light is important to horticulture because each spectrum triggers different responses from the plants—blue light induces vegetative growth, red light induces flowering. This in turn plays into which type of lighting rig you'll use and when—some types specialize in certain parts of the spectrum while others can span multiple wavelengths.

Fluorescent Bulbs

Fluorescent light bulbs are a mainstay of the modern nursery. As stated above, their low heat production makes them ideal for nurturing baby plants (Leaf lettuce, spinach, and herbs also do very well under tubes).

Pros

Inexpensive to purchase

Inexpensive to operate

Long service life—roughly 10-20 times that of an incandescent bulb

Low heat production

Cons

Florescents produce a narrow spectrum of cool light that is unsuitable for triggering the flowering response in plants.

Metal Halide (MH)

Metal halide, or MH, produces cool light in the range of 2700 to 5500 Kelvin and very closely mimics natural light (partly why MH bulbs are becoming increasingly popular in public venues). This, of course, also makes it an obvious choice for promoting vegetative growth. Horticultural versions are even available that also shine in the red spectrum as well.

Pros

Very close to the spectrum of natural sunlight (6000K)

Effective for promoting vegetative growth

Long life span—lasting five times longer than incandescents (15,000 hours)

Cons

They suck down a lot of power—250-1000 watts for average ballasts

They operate under extremely high pressures (up to 20 atmospheres) and require special ballasts

MH bulbs require a few minutes to warm up when initially switched on

MH rigs: bulb, ballast, etc are not cheap, running into the thousands

High Pressure Sodium (HPS)

If you want something to flower or bear fruit, stick it under a High Pressure Sodium lamp. HPS rigs produce light in the warm, red end of the spectrum which is a nearly universal reproductive trigger in the plant world. The corollary is that it does a piss-poor job of actually growing plants—they end up all gangly and scraggly if raised under only red light.

Pros

Superior flower production compared to MH or Florescent

High energy efficiency - six times more light per watt output than an incandescent.

Cons

Grows taller, wispier plants

Plants appear washed out and nitrogen-starved due to the bulb's poor color rendering (how accurately it depicts various colors of llight)

Light Emitting Diodes (LED)

LEDs are new on the scene but could well be the future of indoor grow operations. They work like any other LED light, a bunch of low-wattage LEDs are arrayed on a circuit board and produce light. LEDs are, unlike other High Intensity Discharge (HID) rigs, exceedingly energy efficient. This is because they're capable of producing the exact wavelength of light desired and no other. This means that an LED light programmed to shine at 5700K will shine at that an no other. Some LED rigs are also able to produce light at two distinct spectrum point simultaneously without any bleeding into other inefficient wavelengths and minimal heat production.

Pros

Can produce dual band color spectrum (red and blue) at the same time

Highly energy-efficient—nearly all wattage is converted into usable light

Minimal heat production reduces A/C and heat sink costs

Cons

Expensive to purchase—LED rigs can cost as much as large HID assemblies yet deliver light to less square-footage